Combine the water, dashi powder, sake, mirin, soy sauce, sugar, and sesame oil in a large cup and set aside.
1 cup water, 1.5 Tbsp instant dashi soup stock, 3 Tbsp sake, ¼ cup mirin, 6 Tbsp soy sauce, 2 Tbsp granulated sugar, 1 tsp sesame oil
In a large skillet, add the sliced onion and saute for about 1 minute just to soften it up. Pour in the broth mixture and simmer, covered, for 1-2 minutes.
1 yellow onion
Add the beef and simmer uncovered for 3-4 minutes, until the beef is cooked through and the onions are tender.
1 pound thinly sliced beef
Garnish with chopped green onions and a poached egg, then serve over a bed of white rice.
Chopped green onions, Poached egg, White rice